Cadmium

Primary reference(s)

WHO, 2019. Preventing disease through healthy environments – Exposure to cadmium: A major
public health concern. World Health Organization (WHO). Accessed 25 November 2019.

Additional scientific description

Cadmium (chemical symbol Cd, atomic number 48) is an element that exists as a number of compounds due to it combining with other elements, including oxygen to form cadmium oxide, chlorine to form cadmium chloride, or sulphur to form cadmium sulphide and cadmium sulphate. Cadmium oxide and cadmium sulphide are most commonly found in the air, whereas cadmium chloride and cadmium sulphate dissolve in water (PHE, 2016).

Cadmium is generally present in the environment at low levels; however, human activity has greatly increased levels in environmental media relevant to population exposure. Cadmium can travel long distances from the source of emission by atmospheric transport. It is readily accumulated in many organisms, notably molluscs and crustaceans. Lower concentrations are found in vegetables, cereals and starchy roots (WHO, 2019). Cadmium compounds can be released to the environment in a number of ways, including:

• Natural activities, such as volcanic activity (both on land and in the deep sea), weathering and erosion, and river transport (WHO, 2019).
• Human activities, such as tobacco smoking, mining, smelting and refining of non-ferrous metals, fossil fuel combustion, incineration of municipal waste (especially cadmium-containing batteries and plastics), use of cadmium containing phosphate fertilisers, and recycling of cadmium-plated steel scrap and electric and electronic waste (WHO, 2019).
• Remobilisation of historic sources, such as the contamination of watercourses by drainage water from metal mines or from waste sites (WHO, 2019).

Cadmium exerts toxic effects on the kidney, the skeletal system and the respiratory system and is classified as a human carcinogen (IARC, 1993). Osteomalacia (softening of the bones) and osteoporosis may occur in those exposed through living or working in cadmium-contaminated areas; for example, in an area of Japan where water and soil were contaminated with cadmium from zinc/lead mines, itai-itai (‘ouch-ouch’) disease (characterised by osteomalacia, osteoporosis, painful bone fractures and kidney dysfunction) used to be widespread (WHO, 2019).

Human exposure occurs mainly from consumption of contaminated food, active and passive inhalation of tobacco smoke, and inhalation by workers in a range of industries. National, regional and global actions are needed to decrease global environmental cadmium releases and reduce occupational and environmental exposure (WHO, 2019).

Metrics and numeric limits

The World Health Organization (WHO) has published cadmium guidelines for provisional tolerable monthly intake levels, drinking-water and air (WHO, 2019).

• Provisional tolerable monthly intake: The Joint Food and Agriculture Organization of the United Nations (FAO)/WHO Expert Committee on Food Additives (JECFA) established a provisional tolerable monthly intake for cadmium in 2010 of 25 μg/kg body weight, based on meta-analysis of epidemiological studies on the relationship between urinary cadmium and beta- 2-microglobulin (a marker of renal tubular effects). In light of the long half-life of cadmium in humans, JECFA decided to express the tolerable intake as a monthly value.
• Drinking-water: The guideline for cadmium in drinking-water is 3 μg/l.
• Air: The guideline for cadmium in air is 5 ng/m3 (annual average).

Examples of drivers, outcomes and risk management

Cadmium contained in soil and water can be taken up by certain crops and aquatic organisms and accumulate in the food chain. Food constitutes the main environmental source of cadmium for non-smokers. Highest cadmium levels are found in the kidney and liver of mammals when fed with cadmium-contaminated feed, and in certain species of oyster, scallop, mussel and crustacean (WHO, 2019).

The tobacco plant naturally accumulates relatively high concentrations of cadmium in its leaves. Thus, smoking tobacco is an important source of exposure and – in the case of heavy smokers – daily intake may exceed that from food. Cigarette smoking can cause significant increases in the concentration of cadmium in the kidney, the main target organ for cadmium toxicity (WHO, 2019).

Inexpensive jewellery, toys and plastics can be significant sources of exposure to cadmium, especially for children; however, many countries have moved to restrict or ban cadmium in such products (WHO, 2019).

In terms of occupational exposure through industrial processes, principal uses are currently in nickel-cadmium batteries, pigments, coatings and plating, as a stabiliser in plastics and other materials (including non-ferrous alloys, semiconductors and photovoltaic devices). The highest potential occupational exposures occur in cadmium production and refining, nickelcadmium battery manufacture, cadmium pigment manufacture and formulation, cadmium alloy production, mechanical plating, zinc smelting, brazing with silver-cadmium-silver alloy solder and polyvinylchloride compounding (WHO, 2019).

The WHO factsheet on preventing disease through healthy environments (WHO, 2019) includes the following risk mitigation recommendations:

• Implement the WHO Framework Convention on Tobacco Control, including providing for protection from exposure to tobacco smoke in indoor workplaces, public transport, indoor public places and, as appropriate, other public places (WHO, 2003).
• Reduce, as far as is practicable, emissions of cadmium – particularly into surface waters – from mining and smelting, waste incineration, application of sewage sludge to the land, and use of phosphate fertilisers and cadmium-containing manure. Develop techniques for the safe disposal of cadmium-containing wastes and effluents.
• Washing fruit and vegetables and peeling roots and tubers can help reduce cadmium contamination.
• Promote safe and effective measures to increase recycling of cadmium and to restrict non-recyclable uses.
• Promote the elimination of use of cadmium in products such as toys, jewellery and plastics.
• Reduce cadmium exposure by, for instance, improving working conditions in the non-ferrous metal smelting industry and disseminating information on the proper selection of fertilisers (which sometimes contain high levels of cadmium).
• Raise global awareness on the importance of minimising waste discharges of cadmium.